c# first try

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;

namespace _1._1
{
    class Program
    {
        static void CreateArray(int n, ref int[] arr)
        {
            Random r = new Random();
            Thread.Sleep(1);

            for (int i = 0; i < n; i++)
            {
                Array.Resize(ref arr, i + 1);
                arr[i] = r.Next(1000);
            }

            foreach (int item in arr)
                Console.Write(item + " ");
        }

        /*        static int[] test()
                {
                    int[] nums = new int[40];
                    for (int i = 0; i < 40; i++)
                        nums[i] = i + 1;
                    return nums;
                } */


        static double[] CreateArray1(ref double[] newarr)
        {
            int n = 10;
            Array.Resize(ref newarr, n);
            newarr[0] = 1;

            for (int i = 1; i < n; i++)
            {
                newarr[i] = newarr[i - 1] * (-1.0/(2 * i + 1));
            }

                  foreach (double item in newarr)
                     Console.WriteLine("{0:f5} ", item);
            return newarr;
        }


        static void Main()
        {
            //         int n = 10;
            //     int[] arr = new int[0];

            //   CreateArray1(n, ref arr);
            double[] newarr = new double[0];

            CreateArray1(ref newarr);
        }
    }
}